Influence of Er3+ substitution on the structural, magnetic, and magnetostrictive properties of cobalt ferrite synthesized from spent Li-ion batteries

This study presents the effect of Er3+ substitution for Fe3+ at low concentrations on the structural, magnetic, and magnetostrictive properties of cobalt ferrite synthesized by sol-gel method using spent Li-ion batteries as raw materials. The XRD results confirm the formation of pure-phase cubic spinel structure with average crystallite sizes of 24.8-41.5 nm as obtained through the Scherrer formula. Although Er3+ substitution does not show any observable changes in morphology, the magnetic and magnetostrictive properties are strongly affected. Density measurements obtained by the Archimedes method reveal that the bulk density decreases and the porosity increases with Er3+ substitution because of the formation of intragranular pores during sintering. The saturation magnetization and coercivity of the samples obtained with a vibrating sample magnetometer are influenced by the incorporation of Er3+ at the B-sites. Magnetostriction and strain derivative curves show that Er3+ substitution makes cobalt ferrite more suitable for advanced magnetomechanical stress sensors and energy-efficient actuator devices.